This invention relates to magnetic tape cassettes, and more specifically to compact magnetic tape cassettes which are equal to or smaller than the "Philips" type magnetic tape cassette in size and can be used for audio devices or the like.
Recently, cassette tape recorders have been remarkably reduced both in size and in weight, and accordingly magnetic tape cassettes used for them have also been miniaturized and have become quite popular. In this connection, there has been a strong demand for the provision of a magnetic tape cassette which is suitable for high quality and high density signal recording and reproducing and which will have a long useful life. As is well known in the art, these criteria can be satisfied by employing a digital system such as a pulse code modulation (PCM) system. In a PCM system, unlike an analog system, the recording and reproducing operation is carried out with the input signal pulse-modulated. Furthermore, in the digital system, it is essential that the magnetic tape of the magnetic tape cassette have a recording frequency band which is about five times as wide as a recording frequency band for a conventional audio magnetic tape. For this reason, a large video tape cassette, which is wider in recording frequency band than an audio compact cassette, is extensively employed as a magnetic tape cassette in a digital system. Video tape cassettes, except for special ones, are for rotary head type video tape recorders. The structure of the video tape cassette is such that a guard panel is provided which can close the opening formed in the front part of the cassette and which can swing open upwardly.
In cassettes employing the digital system, as in video tape cassettes, the cassette should be so constructed that it is excellent in dust-proof and tape protection characteristics because the recording and reproduction operation in digital tape cassettes is shorter in recording wavelength, higher in recording density, and wider in frequency band than in conventional audio compact cassettes.
A magnetic tape cassette satisfying the above-described requirements, i.e., a magnetic tape cassette to which the technical concept of the invention is applicable, can be used for audio devices or the like which employ a recording and reproducing system with a relatively wide frequency band, similar to the above-described video tape cassette. Since the compact magnetic tape cassette to which the technical concept of the invention is applicable is small, that is, one which is equal to or smaller than a conventional audio compact cassette, it is expected that the compact magnetic tape cassette will be carried and used outdoors as frequently as, if not more frequently than, the conventional audio compact cassette. Accordingly, the magnetic tape cassette should be constructed with an excellent dust-proof mechanism, which does not adversely affect operation. In addition, the magnetic tape cassette should be constructed so as to positively prevent tape jamming which might occur due to the tape being slackened due to vibration of the cassette during transportation.